Physical chemistry is the study of
macroscopic
The macroscopic scale is the length scale on which objects or phenomena are large enough to be visible with the naked eye, without magnifying optical instruments. It is the opposite of microscopic.
Overview
When applied to physical phenomena a ...
and
microscopic phenomena in
chemical
A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., w ...
systems in terms of the principles, practices, and concepts of
physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...
such as
motion,
energy,
force,
time
Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, ...
,
thermodynamics,
quantum chemistry,
statistical mechanics,
analytical dynamics and
chemical equilibria.
Physical chemistry, in contrast to
chemical physics
Chemical physics is a subdiscipline of chemistry and physics that investigates physicochemical phenomena using techniques from atomic and molecular physics and condensed matter physics; it is the branch of physics that studies chemical process ...
, is predominantly (but not always) a supra-molecular science, as the majority of the principles on which it was founded relate to the bulk rather than the molecular or atomic structure alone (for example, chemical equilibrium and
colloids
A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend ...
).
Some of the relationships that physical chemistry strives to resolve include the effects of:
#
Intermolecular force
An intermolecular force (IMF) (or secondary force) is the force that mediates interaction between molecules, including the electromagnetic forces of attraction
or repulsion which act between atoms and other types of neighbouring particles, e.g. ...
s that act upon the physical properties of materials (
plasticity,
tensile strength,
surface tension in
liquids).
#
Reaction kinetics on the
rate of a reaction.
# The identity of ions and the
electrical conductivity of materials.
#
Surface science and
electrochemistry of
cell membranes.
# Interaction of one body with another in terms of quantities of
heat
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...
and
work
Work may refer to:
* Work (human activity), intentional activity people perform to support themselves, others, or the community
** Manual labour, physical work done by humans
** House work, housework, or homemaking
** Working animal, an animal t ...
called
thermodynamics.
# Transfer of heat between a chemical system and its surroundings during change of
phase or
chemical reaction
A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...
taking place called
thermochemistry
Thermochemistry is the study of the heat energy which is associated with chemical reactions and/or phase changes such as melting and boiling. A reaction may release or absorb energy, and a phase change may do the same. Thermochemistry focuses on ...
# Study of
colligative properties of number of species present in solution.
# Number of phases, number of components and degree of freedom (or variance) can be correlated with one another with help of
phase rule
In thermodynamics, the phase rule is a general principle governing "pVT" systems, whose thermodynamic states are completely described by the variables pressure (), volume () and temperature (), in thermodynamic equilibrium. If is the number of d ...
.
# Reactions of
electrochemical cell
An electrochemical cell is a device capable of either generating electrical energy from chemical reactions or using electrical energy to cause chemical reactions. The electrochemical cells which generate an electric current are called voltaic o ...
s.
# Behaviour of microscopic systems using
quantum mechanics
Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistr ...
and macroscopic systems using
statistical thermodynamics
In physics, statistical mechanics is a mathematical framework that applies statistical methods and probability theory to large assemblies of microscopic entities. It does not assume or postulate any natural laws, but explains the macroscopic b ...
.
Key concepts
The key concepts of physical chemistry are the ways in which pure
physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...
is applied to chemical problems.
One of the key concepts in classical chemistry is that all
chemical compounds
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
can be described as groups of
atoms bonded together and
chemical reactions can be described as the making and breaking of those bonds. Predicting the properties of chemical compounds from a description of atoms and how they bond is one of the major goals of physical chemistry. To describe the atoms and bonds precisely, it is necessary to know both where the
nuclei of the atoms are, and how electrons are distributed around them.
[Atkins, Peter and Friedman, Ronald (2005). ''Molecular Quantum Mechanics'', p. 249. ]Oxford University Press
Oxford University Press (OUP) is the university press of the University of Oxford. It is the largest university press in the world, and its printing history dates back to the 1480s. Having been officially granted the legal right to print books ...
, New York. .
Disciplines
Quantum chemistry, a subfield of physical chemistry especially concerned with the application of
quantum mechanics
Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistr ...
to chemical problems, provides tools to determine how strong and what shape bonds are,
how nuclei move, and how light can be absorbed or emitted by a chemical compound.
Spectroscopy is the related sub-discipline of physical chemistry which is specifically concerned with the interaction of
electromagnetic radiation with matter.
Another set of important questions in chemistry concerns what kind of reactions can happen spontaneously and which properties are possible for a given chemical mixture. This is studied in
chemical thermodynamics
Chemical thermodynamics is the study of the interrelation of heat and work with chemical reactions or with physical changes of state within the confines of the laws of thermodynamics. Chemical thermodynamics involves not only laboratory measurem ...
, which sets limits on quantities like how far a reaction can proceed, or how much
energy can be converted into work in an
internal combustion engine
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal c ...
, and which provides links between properties like the
thermal expansion coefficient and rate of change of
entropy with
pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
for a
gas
Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma).
A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...
or a
liquid. It can frequently be used to assess whether a reactor or engine design is feasible, or to check the validity of experimental data. To a limited extent,
quasi-equilibrium and
non-equilibrium thermodynamics
Non-equilibrium thermodynamics is a branch of thermodynamics that deals with physical systems that are not in thermodynamic equilibrium but can be described in terms of macroscopic quantities (non-equilibrium state variables) that represent an ext ...
can describe irreversible changes.
[Hill, Terrell L. (1986). ''Introduction to Statistical Thermodynamics'', p. 1. Dover Publications, New York. .] However, classical thermodynamics is mostly concerned with systems in
equilibrium and
reversible changes and not what actually does happen, or how fast, away from equilibrium.
Which reactions do occur and how fast is the subject of
chemical kinetics, another branch of physical chemistry. A key idea in chemical kinetics is that for
reactants to react and form
products
Product may refer to:
Business
* Product (business), an item that serves as a solution to a specific consumer problem.
* Product (project management), a deliverable or set of deliverables that contribute to a business solution
Mathematics
* Produ ...
, most chemical species must go through
transition states which are higher in
energy than either the reactants or the products and serve as a barrier to reaction. In general, the higher the barrier, the slower the reaction. A second is that most chemical reactions occur as a sequence of
elementary reaction
An elementary reaction is a chemical reaction in which one or more chemical species react directly to form products in a single reaction step and with a single transition state. In practice, a reaction is assumed to be elementary if no reaction ...
s, each with its own transition state. Key questions in kinetics include how the rate of reaction depends on temperature and on the concentrations of reactants and
catalysts
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
in the reaction mixture, as well as how catalysts and reaction conditions can be engineered to optimize the reaction rate.
The fact that how fast reactions occur can often be specified with just a few concentrations and a temperature, instead of needing to know all the positions and speeds of every molecule in a mixture, is a special case of another key concept in physical chemistry, which is that to the extent an engineer needs to know, everything going on in a mixture of very large numbers (perhaps of the order of the
Avogadro constant, 6 x 10
23) of particles can often be described by just a few variables like pressure, temperature, and concentration. The precise reasons for this are described in
statistical mechanics,
[Chandler, David (1987). ''Introduction to Modern Statistical Mechanics'', p. 54. Oxford University Press, New York. .] a specialty within physical chemistry which is also shared with physics. Statistical mechanics also provides ways to predict the properties we see in everyday life from molecular properties without relying on empirical correlations based on chemical similarities.
History
The term "physical chemistry" was coined by
Mikhail Lomonosov in 1752, when he presented a lecture course entitled "A Course in True Physical Chemistry" () before the students of
Petersburg University. In the preamble to these lectures he gives the definition: "Physical chemistry is the science that must explain under provisions of physical experiments the reason for what is happening in complex bodies through chemical operations".
Modern physical chemistry originated in the 1860s to 1880s with work on
chemical thermodynamics
Chemical thermodynamics is the study of the interrelation of heat and work with chemical reactions or with physical changes of state within the confines of the laws of thermodynamics. Chemical thermodynamics involves not only laboratory measurem ...
,
electrolytes in solutions,
chemical kinetics and other subjects. One milestone was the publication in 1876 by
Josiah Willard Gibbs of his paper, ''
On the Equilibrium of Heterogeneous Substances''. This paper introduced several of the cornerstones of physical chemistry, such as
Gibbs energy
In thermodynamics, the Gibbs free energy (or Gibbs energy; symbol G) is a thermodynamic potential that can be used to calculate the maximum amount of work that may be performed by a thermodynamically closed system at constant temperature and pre ...
,
chemical potentials, and
Gibbs' phase rule
In thermodynamics, the phase rule is a general principle governing "pVT" systems, whose thermodynamic states are completely described by the variables pressure (), volume () and temperature (), in thermodynamic equilibrium. If is the number of d ...
.
The first
scientific journal specifically in the field of physical chemistry was the German journal, ''
Zeitschrift für Physikalische Chemie'', founded in 1887 by
Wilhelm Ostwald
Friedrich Wilhelm Ostwald (; 4 April 1932) was a Baltic German chemist and philosopher. Ostwald is credited with being one of the founders of the field of physical chemistry, with Jacobus Henricus van 't Hoff, Walther Nernst, and Svante Arrhen ...
and
Jacobus Henricus van 't Hoff. Together with
Svante August Arrhenius, these were the leading figures in physical chemistry in the late 19th century and early 20th century. All three were awarded the
Nobel Prize in Chemistry between 1901 and 1909.
Developments in the following decades include the application of
statistical mechanics to chemical systems and work on
colloids and
surface chemistry
Surface science is the study of physical and chemical phenomena that occur at the interface of two phases, including solid–liquid interfaces, solid– gas interfaces, solid–vacuum interfaces, and liquid– gas interfaces. It includes the fi ...
, where
Irving Langmuir made many contributions. Another important step was the development of
quantum mechanics
Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistr ...
into
quantum chemistry from the 1930s, where
Linus Pauling was one of the leading names. Theoretical developments have gone hand in hand with developments in experimental methods, where the use of different forms of
spectroscopy, such as
infrared spectroscopy,
microwave spectroscopy
Microwave spectroscopy is the spectroscopy method that employs microwaves, i.e. electromagnetic radiation at GHz frequencies, for the study of matter.
History
The ammonia molecule NH3 is shaped like a pyramid 0.38 Å in height, with an equilatera ...
,
electron paramagnetic resonance and
nuclear magnetic resonance spectroscopy
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique to observe local magnetic fields around atomic nuclei. The sample is placed in a magnetic fie ...
, is probably the most important 20th century development.
Further development in physical chemistry may be attributed to discoveries in
nuclear chemistry, especially in isotope separation (before and during World War II), more recent discoveries in
astrochemistry
Astrochemistry is the study of the abundance and reactions of molecules in the Universe, and their interaction with radiation. The discipline is an overlap of astronomy and chemistry. The word "astrochemistry" may be applied to both the Solar Syst ...
,
as well as the development of calculation algorithms in the field of "additive physicochemical properties" (practically all physicochemical properties, such as boiling point, critical point, surface tension, vapor pressure, etc.—more than 20 in all—can be precisely calculated from chemical structure alone, even if the chemical molecule remains unsynthesized), and herein lies the practical importance of contemporary physical chemistry.
See
Group contribution method,
Lydersen method The Lydersen method is a group contribution method for the estimation of critical properties temperature ( Tc), pressure ( Pc) and volume (Vc). The Lydersen method is the prototype for and ancestor of many new models like Joback, Klincewicz,
Ambr ...
,
Joback method,
Benson group increment theory,
quantitative structure–activity relationship
Journals
Some journals that deal with physical chemistry include ''
Zeitschrift für Physikalische Chemie'' (1887); ''
Journal of Physical Chemistry A'' (from 1896 as ''Journal of Physical Chemistry'', renamed in 1997); ''
Physical Chemistry Chemical Physics'' (from 1999, formerly ''
Faraday Transactions'' with a history dating back to 1905); ''
Macromolecular Chemistry and Physics
''Macromolecular Chemistry and Physics'' is a biweekly Peer review, peer-reviewed scientific journal covering polymer science. It publishes full papers, talents, trends, and highlights in all areas of polymer science, from chemistry to physical che ...
'' (1947); ''
Annual Review of Physical Chemistry
''Annual Review of Physical Chemistry'' is a peer-reviewed scientific journal published by Annual Reviews. It covers all topics pertaining to physical chemistry. The editors are Mark A. Johnson (Yale University) and Todd J. Martínez ( Stanfo ...
'' (1950); ''
Molecular Physics
Molecular physics is the study of the physical properties of molecules and molecular dynamics. The field overlaps significantly with physical chemistry, chemical physics, and quantum chemistry. It is often considered as a sub-field of atomic, m ...
'' (1957); ''
Journal of Physical Organic Chemistry
The ''Journal of Physical Organic Chemistry'' is a monthly peer-reviewed scientific journal, published since 1988 by John Wiley & Sons. It covers research in physical organic chemistry in its broadest sense and is available both online and in print ...
'' (1988); ''
Journal of Physical Chemistry B'' (1997); ''
ChemPhysChem'' (2000); ''
Journal of Physical Chemistry C'' (2007); and ''
Journal of Physical Chemistry Letters'' (from 2010, combined letters previously published in the separate journals)
Historical journals that covered both chemistry and physics include ''
Annales de chimie et de physique'' (started in 1789, published under the name given here from 1815 to 1914).
Branches and related topics
*
Chemical thermodynamics
Chemical thermodynamics is the study of the interrelation of heat and work with chemical reactions or with physical changes of state within the confines of the laws of thermodynamics. Chemical thermodynamics involves not only laboratory measurem ...
*
Chemical kinetics
*
Statistical mechanics
*
Quantum chemistry
*
Electrochemistry
*
Photochemistry
*
Surface chemistry
Surface science is the study of physical and chemical phenomena that occur at the interface of two phases, including solid–liquid interfaces, solid– gas interfaces, solid–vacuum interfaces, and liquid– gas interfaces. It includes the fi ...
*
Solid-state chemistry Solid-state chemistry, also sometimes referred as materials chemistry, is the study of the synthesis, structure, and properties of solid phase materials, particularly, but not necessarily exclusively of, non-molecular solids. It therefore has a str ...
*
Spectroscopy
*
Biophysical chemistry
*
Materials science
*
Physical organic chemistry
Physical organic chemistry, a term coined by Louis Hammett in 1940, refers to a discipline of organic chemistry that focuses on the relationship between chemical structures and reactivity, in particular, applying experimental tools of physical c ...
*
Micromeritics The term micromeritics was given to the science and technology of small particles by J. M. DallaValle. It is thus the study of the fundamental and derived properties of individual as well as a collection of particles. The knowledge and control of th ...
See also
*
List of important publications in chemistry#Physical chemistry
*
List of unsolved problems in chemistry#Physical chemistry problems
*
Physical biochemistry
*
:Physical chemists
References
External links
The World of Physical Chemistry(Keith J. Laidler, 1993)
Physical Chemistry from Ostwald to Pauling(John W. Servos, 1996)
(Joachim Schummer, ''The Autonomy of Chemistry'', Würzburg, Königshausen & Neumann, 1998, pp. 135–148)
The Cambridge History of Science: The modern physical and mathematical sciences(Mary Jo Nye, 2003)
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